The present invention is related to the field of power supply regulators, and more specifically to the field of power supply regulators which control two or more independently operative power supplies by providing separate pulse width modulation control signals thereto.
Power supply control systems exist wherein a regulator controls a power supply output by creating a pulse width modulation control signal. Such power supply control systems are referred to as switchmode regulator controlled power supplies and custom integrated circuit control circuits for these power supplies exist, such as integrated circuit MC3420 manufactured by Motorola, Inc. and integrated circuit SG1524 manufactured by Signetics Corporation. Typically in such systems, a periodic, variable amplitude carrier signal is generated by a power supply control circuit and this variable amplitude carrier signal is subsequently utilized to provide a pulse width modulated signal that is used to control the excitation of a power supply. The output of the power supply is then sampled by a voltage or current sensing circuit, compared to a predetermined voltage or current reference level to create an analog error signal, and the error signal is utilized to control the amount of pulse width modulation to thereby maintain the output of the power supply at a constant desired level.
Typically, the periodic carrier signal provided by the switchmode regulator control circuit will have either a triangle or ramp waveshape having a period T, and the regulator will provide pulse width modulated, variable duration output control pulses and these pulses are used to control, and therefore regulate, the excitation of the power supply. Typically, a single pulse width modulated, variable duration drive pulse is provided during each period T and two output drive signals are derived therefrom each operative during alternate sequential periods T to provide power supply excitation control signals. Normally the two output drive signals are utilized to control a push-pull mode power supply drive circuit, but these drive signals can also be used to sequentially excite a single power supply drive device. In either event a single variable duration pulse produced by pulse width modulation techniques is produced for each period T and this signal is used to control the excitation, and therefore the output, of a power supply.
It has been previous proposed to utilize the pulse width regulator ramp carrier signal of the Signetics Corporation integrated circuit SG1524 to produce two control signals having alternately occurring but independent variable duration drive pulses for separate control of two independently operative power supplies. This is accomplished by providing two error signals, one related to the difference between a first power supply output and a first reference level and the other error signal related to the difference between a second power supply output and a second reference level. Each error signal is then utilized to provide a variable duration drive pulse, by use of pulse modulation techniques, wherein during each period T of the carrier signal a power supply drive pulse for either the first or the second power supply is produced. Thus, as was the case for providing the control signals for a single power supply, during each period T of the carrier wave only a single power supply drive signal pulse is provided, but now the control pulses provided in alternate periods T are used to control a first power supply while alternate periodic pulses provided between these first power supply pulses are used to control a second power supply. Thus the excitation control pulses for any one power supply have a period of 2T.
The above described structure does result in utilizing the same carrier signal for providing two independent pulse width modulation output drive signals that have alternately produced drive pulses. This insures that each of the drive signals produced for each power supply will occur sequentially and not simultaneously and this therefore reduces the amount of peak current for power supply energization that will have to be utilized at any one instant. However, the cost of standard power supply regulator circuits which provide a single variable duration drive pulse during each period T of the carrier signals is substantial, and this would therefore discourage the use of such circuitry for providing separately operative power supply regulation for two independently operative power supplies in a regulation system as described above. In addition, if two separately operative power supplies are to be controlled according to the above structure, the frequency of the carrier wave must be relatively high to insure proper operation of the regulator circuit since for each power supply a pulse width modulation drive pulse is provided only during alternate cycles of the carrier and if too much time elapses between power supply excitation pulses the output of the power supply may not be maintainable at a desired level with the use of relatively inexpensive power supply components, and use of too low of a frequency for the carrier wave can result in audible noise due to the magnetostrictive operation of transformers used in the power supply. The use of a too high of a frequency for the carrier signal to overcome the previously mentioned problems should be avoided since this may create design and power dissipation problems as well as possibly causing radiation of the high frequency carrier signal resulting in undesired noise.